The present invention relates to operating vacuum tubes at lower than the normally specified plate or screen grid voltages. The present invention is related to voltage controlled resistors.
Specially made tubes (e.g., including low voltage space charge tubes that operates at about 12 volts on the plates and or screen grid or space charge grid) such as those manufactured for automobiles in the 1950s allowed for low plate voltages. However, conventionally manufactured vacuum tubes require high voltages. The specification data sheets of these types of tubes generally require high voltages applied to the plates and or screen grids.